Refrigerator

ABSTRACT

A pulse tube refrigerator has a pulse tube having a first end and a second end. A inertance tube connects the first end and a buffer tank. A pressure change generator is connected with the second end. The pressure change generator generates a pressure change of a working gas at the second end periodically. A first flow straightener provided at the first end. A second flow straightener provided at the second end. A degree to which the first flow straightener hinders the flow of the working gas is greater than a degree to which the second flow straightener hinders the flow of the working gas.

INCORPORATION BY REFERENCE

Priority is claimed to Japanese Patent Application No. 2013-160171, filed Aug. 1, 2013, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a refrigerator equipped with a pulse tube.

2. Description of the Related Art

In the related art, pulse tube refrigerators have been used for cooling an apparatus that requires an ultralow temperature environment.

In pulse tube refrigerators, a regenerator and a low-temperature end of a pulse tube are cooled by repeating an operation in which working gas (for example, helium gas) compressed by a compressor flows into the regenerator and the pulse tube, and an operation in which the working gas is discharged from the pulse tube and collected in the compressor.

The regenerator of the pulse tube refrigerators is constituted by a tubular member (cylinder) having a cold storage material therein. The pulse tube is constituted by a hollow tubular member (cylinder). Low-temperature ends of both the regenerator and the pulse tube communicate with each other through a communication passage. A cooling stage to be connected a cooling object is installed at the low temperature end of the regenerator and the pulse tube.

A pulse tube refrigerator has a flow straightener arranged on a low-temperature end side of a pulse tube.

SUMMARY

According to an embodiment of the present invention, there is provided a pulse tube refrigerator. A pulse tube has a first end and a second end. A inertance tube connects the first end and a buffer tank. A pressure change generator is connected with the second end. The pressure change generator generates a pressure change of a working gas at the second end periodically. A first flow straightener is provided at the first end. A second flow straightener is provided at the second end. a degree to which the first flow straightener hinders the flow of the working gas is greater than a degree to which the second flow straightener hinders the flow of the working gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the configuration of a pulse tube refrigerator related to an embodiment.

FIG. 2 is a schematic configuration view of a high-temperature-side flow straightener.

FIG. 3 is an equivalent PV chart obtained by calculation regarding a pulse tube that has no flow straightener.

FIG. 4 is a graph showing the relationship between the ratio of the flow path resistance of the flow straightener, and the refrigeration capacity of the pulse tube refrigerator.

DETAILED DESCRIPTION

Some pulse tube refrigerators have an inertance tube connected to the high-temperature end of the pulse tube as a phase controller. Although the operation of the pulse tube refrigerators includes a phase in which room temperature working gas flows into the pulse tube from an inertance tube. At the phase, thermal loss may increase if the room temperature working gas that has flowed into the low temperature end side.

It is desirable to improve the refrigeration capacity of a pulse tube refrigerator.

In addition, arbitrary combinations of the above constituent elements, and those obtained by substituting the constituent elements or expressions of the invention with each other between apparatuses, methods, and systems, or the like are also effective as the aspects of the invention.

According to the embodiment of the invention, the refrigeration capacity of the pulse tube refrigerator can be enhanced.

Hereinafter, the same or equivalent constituent elements and members shown in respective drawings will be designated by the same reference numerals, and duplicate description will be omitted appropriately. Additionally, the dimensions of the members in the respective drawings are appropriately shown in an enlarged or contracted manner in order to make the invention easily understood. Additionally, when an embodiment is described in the respective drawings, some of members that are not important will be omitted.

FIG. 1 is a schematic view showing the configuration of a pulse tube refrigerator 100 related to an embodiment. The pulse tube refrigerator 100 is an in-line type, and includes a compressor 110, an aftercooler 130, a cool storage pipe or a regenerator 120, a pulse tube 140, a cooling stage 180, and a buffer tank 190. The regenerator 120 has a high-temperature end 125 a and a low-temperature end 125 b, and the pulse tube 140 has a high-temperature end 145 a and a low-temperature end 145 b.

The working gas of the pulse tube refrigerator 100 is helium gas. Pressure change of the helium gas generated in the compressor 110 is transmitted to the pulse tube 140 via the aftercooler 130 and the regenerator 120. During the operation of the pulse tube refrigerator 100, a pipe 116, the regenerator 120, the pulse tube 140, an inertance tube 192, and the buffer tank 190 are respectively filled with the helium gas. The compressor 110 includes a first cylinder 112 a, a second cylinder 112 b, a first piston 114 a that moves within the first cylinder 112 a, and a second piston 114 b that moves within the second cylinder 112 b. The first piston 114 a and the second piston 114 b are arranged so as to face each other. Pressure waves are formed in the helium gas within the pipe 116 connecting the first cylinder 112 a and the second cylinder 112 b, according to the movement of the respective pistons 114 a and 114 b. The pipe 116 is connected to the high-temperature end 125 a of the regenerator 120 via the aftercooler 130.

As the two pistons 114 a and 114 b are driven symmetrically in a reciprocal manner with respect to the pipe 116, pressure waves are generated in the pipe 116. More specifically, if the two pistons 114 a and 114 b approach each other, the internal pressure of the pipe 116 becomes high, and the helium gas is delivered from the pipe 116 to the regenerator 120. If the two pistons 114 a and 114 b are kept away from each other, the internal pressure of the pipe 116 becomes low, and the helium gas is drawn into the pipe 116 from the regenerator 120.

The operating frequency of the compressor 110, that is, the frequency of a symmetrical reciprocating motion of the two pistons 114 a and 114 b, is 30 Hz or higher, for example, about 50 Hz. When pressure change is generated not using a valve by basically being (valveless) as in the compressor 110, since it is not necessary to take the response speed of the valve into consideration, the operating frequency can be relatively raised. In contrast, when (valved) pressure change is generated on the basis of the opening and closing of a valve as in a GM type compressor, it is necessary to make the operating frequency relatively low, for example, to be several Hz or lower.

The aftercooler 130 pre-cools the helium gas delivered from the pipe 116 to the high-temperature end 125 a of the regenerator 120. The aftercooler 130 functions as a heat exchanger that realizes heat exchange between the helium gas passing through the aftercooler 130, and a refrigerant (not shown).

The regenerator 120 is constituted by a hollow cylinder 121, and the inside thereof is filled with a cold storage material 122.

The pulse tube 140 includes a hollow cylinder 141, a high-temperature-side flow straightener 149 a provided on the high-temperature end 145 a side of the cylinder 141, and a low-temperature-side flow straightener 149 b provided on the low-temperature end 145 b side of the cylinder 141. The high-temperature-side flow straightener 149 a equalizes the space distribution of the velocity of the helium gas when the helium gas flows into the pulse tube 140 from the inertance tube 192. The low-temperature-side flow straightener 149 b equalizes the space distribution of the velocity of the helium gas when the helium gas flows into the pulse tube 140 from the heat exchanger 182. Hereinafter, the equalization of such velocity distributions is referred to as flow straightening. By performing the flow straightening at the respective end portions of the pulse tube 140, a gas piston to be described below can be stabilized, and the refrigeration performance of the pulse tube refrigerator 100 can be improved.

FIG. 2 is a schematic configuration view of the high-temperature-side flow straightener 149 a. The high-temperature-side flow straightener 149 a has a stacked structure obtained by stacking M (M is a natural number) metal screens 160 having a predetermined mesh or a predetermined mesh number. Accordingly, the metal screens that constitute the high-temperature-side flow straightener 149 a have substantially the same mesh. The M metal screens 160 may be coupled to each other, for example, by diffusion bonding processing.

The “mesh” means the distance (the length of a gap) between adjacent line portions of a metal screen. The “mesh number” means the number of openings per 1 inch (25.4 mm). The “diffusion bonding processing” is a general term of a method in which atomic mutual diffusion occurs at interfaces between the respective metal screens through heating, and thereby, interface joining is performed. Normally, the diffusion bonding processing is performed within a range of 800° C. to 1080° C. (for example, 1000° C.).

The low-temperature-side flow straightener 149 b has a stacked structure obtained by stacking the same N (N is a natural number smaller than M) metal screens as the metal screens 160 that constitute the high-temperature-side flow straightener 149 a. Since N<M is established, a degree (hereinafter, referred to as flow path resistance) to which the high-temperature-side flow straightener 149 a hinders the flow of the helium gas is greater than the degree of flow path resistance of the low-temperature-side flow straightener 149 b.

Referring back to FIG. 1, the low-temperature end 125 b of regenerator 120 is connected with the low-temperature end 145 b of the pulse tube 140 via the heat exchanger 182. The heat exchanger 182 is thermally connected with the cooling stage 180. The heat exchanger 182 exchanges heat between low-temperature helium gas flowing inside the low-temperature end 125 b of the regenerator 120 and the low-temperature end 145 b of the pulse tube 140, and the cooling stage 180. An cooling object (not shown)is thermally connected to the cooling stage 180. During the operation of the pulse tube refrigerator 100, the cooling object is cooled as the heat of the object to be cooled moves into the helium gas via the cooling stage 180 and the heat exchanger 182.

The buffer tank 190 is connected to the high-temperature end 145 a of the pulse tube 140 via the inertance tube 192.

The operation of the pulse tube refrigerator 100 is described below. As the two pistons 114 a and 114 b approach each other, high-pressure helium gas is supplied from the compressor 110 to the aftercooler 130, and is pre-cooled. The pre-cooled high-pressure helium gas is supplied to the regenerator 120. The helium gas that has flowed into the regenerator 120 comes out from the low-temperature end 125 b of the regenerator 120 and passes through the heat exchanger 182 while the helium gas is cooled by the cold storage material 122 and the temperature thereof is lowered. The helium gas flow that has passed through the heat exchanger 182 is straightened by passing through the low-temperature-side flow straightener 149 b provided at the low-temperature end 145 b of the pulse tube 140, and flows into the pulse tube 140.

In this case, the low-pressure helium gas already present in advance inside the pulse tube 140 is compressed by the high-pressure helium gas that has flowed in. Accordingly, the pressure of the helium gas inside the pulse tube 140 becomes higher than the pressure inside the buffer tank 190, and a portion of the helium gas flows into the buffer tank 190 through the inertance tube 192.

Next, if the two pistons 114 a and 114 b are kept away from each other, the helium gas inside the pulse tube 140 passes through the heat exchanger 182 from the low-temperature end 145 b of the pulse tube 140, and flows into the low-temperature end 125 b of the regenerator 120. Moreover, the helium gas passes through the inside of the regenerator 120 while cooling the cold storage material 122, passes through the aftercooler 130 from the high-temperature end 125 a of the regenerator 120, and is collected in the compressor 110.

Here, the pulse tube 140 is connected with the buffer tank 190 via the inertance tube 192. Accordingly, the helium gas is supplied from the buffer tank 190 via the inertance tube 192 to the high-temperature end 145 a of the pulse tube 140, and the helium gas that is supplied in this way is straightened by passing through the high-temperature-side flow straightener 149 a.

A substantially constant phase difference is caused between the phase of a pressure change of the helium gas and the phase of a volume change of the helium gas by the action of the inertance tube 192 and the buffer tank 190. Due to this phase difference, a cooling action caused by the expansion of the helium gas occurs in the low-temperature end 145 b of the pulse tube 140. As the above operation is repeated, the pulse tube refrigerator 100 can cool the object to be cooled that is connected to the cooling stage 180.

In addition, the movement of the helium gas that periodically moves up and down within the pulse tube 140 while maintaining a certain pressure is often referred to as a “gas piston”.

FIG. 3 is an equivalent PV chart obtained by calculation regarding a pulse tube that has no flow straightener. Displacement 62 near a high-temperature end of the pulse tube is made greater than displacement 64 near a low-temperature end. Accordingly, even if the same flow straightener as a flow straightener that exhibits a sufficient flow-straightening action at the low-temperature end is provided at the high-temperature end, a situation in which a flow-straightening action required at the high-temperature end is not exerted may occur.

In contrast, in the pulse tube refrigerator 100 related to the present embodiment, the flow path resistance of the high-temperature-side flow straightener 149 a is greater than the flow path resistance of the low-temperature-side flow straightener 149 b. Thus, a sufficient flow straightening action can be obtained in each of the high-temperature end 145 a and the low-temperature end 145 b. Particularly, the movement of relatively high-temperature (about 300 K) helium gas to the low-temperature end 145 b side can be suppressed during the operation of the pulse tube refrigerator 100 by increasing the flow path resistance of the high-temperature-side flow straightener 149 a. As a result, the heat loss can be suppressed and the refrigeration performance of the pulse tube refrigerator 100 can be improved.

Additionally, when the flow path resistance of a flow straightener is made too high, a negative influence may be exerted on the cooling performance of the pulse tube 140 due to the reduction in the flow straightener. Accordingly, since the low-temperature end 145 b with a relatively low required flow-straightening performance is provided with the low-temperature-side flow straightener 149 b with a relatively low flow path resistance, and the high-temperature end 145 a with a required relatively high flow-straightening action is provided with the high-temperature-side flow straightener 149 a with a relatively high flow path resistance, the cooling performance of the pulse tube 140 can be maximized.

Additionally, in the pulse tube refrigerator 100 related to the present embodiment, the operating frequency of the compressor 110 is 30 Hz or higher. Since the flow velocity when the helium gas flows into the pulse tube 140 from the inertance tube 192 generally becomes greater as the operating frequency becomes higher, the effect of the present embodiment by which the heat loss may be reduced by increasing the flow path resistance of the high-temperature-side flow straightener 149 a becomes more effective as the operating frequency becomes higher.

FIG. 4 is a graph showing the relationship between the ratio of the flow path resistance of the flow straightener, and the refrigeration capacity of the pulse tube refrigerator 100. The data of the graph of FIG. 4 is based on results of experiments performed by the present inventor. The horizontal axis of the graph represents M/N, that is, values obtained by dividing the number of metal screens of the high-temperature-side flow straightener 149 a by the number of metal screens of the low-temperature-side flow straightener 149 b. These values correspond to the values of the ratios of the flow path resistances of the high-temperature-side flow straightener 149 a and the flow path resistance of the low-temperature-side flow straightener 149 b. The mesh number of the metal screens was #250. The vertical axis represents the refrigeration capacity of the pulse tube refrigerator 100 at 77 K in respective M/N when the refrigeration capacity of the pulse tube refrigerator 100 at 77 K in the case of M/N=2 is 1.

As clear from the graph of FIG. 4, the refrigeration capacity becomes maximum near of M/N=6. Particularly, if the range of M/N is 4 to 8, the refrigeration capacity is markedly improved. The same results were also shown in the experiment that was performed with the mesh number set as #300.

The pulse tube refrigerator 100 related to the embodiment is described above. It will be understood by those skilled in the art that this embodiment is merely illustrative, various modification examples are possible by the combinations of the respective constituent elements of the embodiment, and such modification examples are within the scope of the invention.

Although a case where the high-temperature-side flow straightener 149 a and the low-temperature-side flow straightener 149 b are constituted by the metal screens having substantially the same mesh has been described in the embodiment, the invention is not limited to this. For example, the mesh number of the metal screens that constitute the high-temperature-side flow straightener may be made greater than the mesh number of the metal screens that constitute the low-temperature-side flow straightener. According to an experiment performed by the present inventor, when the numbers of screens to be stacked are the same, the refrigeration capacity improved if the ratio (Mesh number of high-temperature-side flow straightener/Mesh number of low-temperature-side flow straightener) of the mesh numbers was made to be within a range of 5 to 12. Additionally, for example, the flow straightener maybe constituted not by the metal screens but by porous bodies.

It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention. 

What is claimed is:
 1. A pulse tube refrigerator, comprising: a pulse tube having a first end and a second end; a inertance tube connecting the first end and a buffer tank; a pressure change generator connected with the second end, configured to generating a pressure change of a working gas at the second end periodically; a first flow straightener provided at the first end; a second flow straightener provided at the second end; and wherein a degree to which the first flow straightener hinders the flow of the working gas is greater than a degree to which the second flow straightener hinders the flow of the working gas.
 2. The pulse tube refrigerator according to claim 1, wherein a frequency of the pressure change is 30 Hz or higher.
 3. The pulse tube refrigerator according to claim 1, wherein a value obtained by dividing the degree to which the first flow straightener hinders the flow of the working gas by the degree to which the second flow straightener hinders the flow of the working gas is within a range of 4 to
 8. 4. The pulse tube refrigerator according to claim 1, wherein, the second flow straightener has a stacked structure in which N metal screens having the substantially same mesh are stacked, and the first flow straightener has a stacked structure in which M metal screens having the substantially same mesh as the mesh of the metal screens are stacked, wherein M is a natural number and N is a natural number greater than N. 